The plasma decay of radiolabeled apolipoprotein A-I and apolipoprotein A-II was analyzed in 14 normal individuals. The residence time of A-II was greater than A-I (p less than 0.005) indicating that A-I decays faster than A-II. Compartmental models were constructed separately for A-I which contained two plasma compartments, one decarying faster than the other. However, only a single plasma compartment was required for the A-II compartmental model. The extra plasma compartment in A-I was found to account for the decrease in A-I residence time. Triglyceride kinetics were studied in 59 normal or hypertriglyceridemic men utilizing radiolabeled glycerol. Analysis by a compartmental model revealed two pathways for the synthesis of VLDL-TG from glycerol. Differences in VLDL-TG kinetics found using 14C-glycerol and 3H-glycerol were related to differences in the kinetics of 14C glycerol as compared to 3H glycerol in only one of the synthesis pathways for VLDL-TG. Triglyceride kinetics were determined in male, obese, nondiabetic Pima Indians and were compared to normal weight, or obese nondiabetic male caucasian controls. By compartmental analysis, the FCR's for VLDL-TG were as follows: .42 hr. obese Indians; .21 hr. normal weight caucasians; and .32 hr. for obese caucasian.